DHCP Fails to Assign DNS/WINS
The Issue
A few months ago a client came in from another part of the business and had an issue where the DHCP server appeared to not have given the PC any DNS entries. This of course was a big problem – DNS is critical to any PC wanting to talk outside of its own broadcast domain. I only had limited time to find a solution to the issue so I had to put together a work-around before coming to the root cause. The work-around was simple enough – Manually supply the DNS addresses and move on. But before the client left I managed to take a Wireshark packet capture of the DHCP event, and sure enough the DNS server addresses were definitely in both the DHCP offer and client response. So something was wrong with the clients’ PC.
All my research turned up was people with similar issues and no real pattern other than a certain sub-set of NIC chipsets. So when I saw it pop up again this week on a HP workstation I immediately got excited about the possibility of nailing this bastard of a problem. I recorded the NIC chipset details and went to work on isolating the issue. I first had to make sure this was really the weird DHCP problem described earlier – I made sure it wasn’t some DHCP scoping problem or an AD group policy of some sort, and finally I did a Wireshark capture. Sure enough, the DNS server addresses were definitely in there. So again, the PC knew about the DNS server address, but it just didn’t apply them. Why?
Luckily, after a lot of Googling I believe I’ve found the fix…
The Root Cause
The root cause appears to be Windows XP SP3. Take special note of ‘SP3′, as it appears to be the only service pack affected. The other contributor is the Lucent QIP DHCP server application – Although there are reports of other DHCP servers causing the same issue, it seems QIP is the largest one affected. Here is an excerpt from the MS Forums explaining the issue:
The investigation shows that the position of the option 43 in the packet seems to be the source of the problem. The XP SP3 client assumes that this will be the last one in the list of options. In most of the cases this is present at the end of the list, but with Lucent’s DHCP Server this option can be placed anywhere in the list of options. That seems to be confusing the XP SP3 client and therefore some options are getting dropped.
The Solution
The solution is quite simple – The KB953761 Hotfix. Unfortunately MS have chosen not to publicly publish this hotfix for whatever reason and you have to contact them directly here.
For me, the real solution is to upgrade the DHCP server – Seriously, if you’re having this issue I’m 95% sure your DHCP server is WAY to old to be in service now. Some people might ask – Why upgrade the DHCP service if its MS’s fault? Sure, but chances are you’re organization is wasting more money keeping the thing managed and alive.